The role and responsibilities of engineersand agriculturalists in reducing vector-borne disease hazardsby A. Kandiah

(Adapted from Axtell, R. c., Priciples of integrated pest management([PM) in relation to mosquito control, Mosquito News 39, pp709-18,1979.)

Health components should be integrated into theoverall planning, development and managementphases of irrigation projects.

The expansion of irrigatedagriculture through appropriatedevelopment and the managementof natural resources is recognizedas a most important strategy toincrease food production incountries where the humanpopulation exceeds (or will shortlyexceed) the low-input supportingcapacity of their land resources.During the past two decades,

increased outbreaks of water-bornediseases such as malaria andschistosomiasis associated withirrigation development, have beena focus for international concern.Analysis of the situation hasrevealed that most of the health-related problems could have beenmitigated or eliminated, hadenvironmental and public healthconsiderations been an integral partof the planning, design andoperation of irrigation projects.In the past (and in some countries

at present), agricultural andirrigation development projectshave been planned, implementedand operated by technicalspecialists, normally agriculturalistsand engineers, who worked mainlywithin their specialities. Social,cultural or public health data wererarely considered in the planning,design or operation.In the context of the present

world food situation, we cannotafford to make mistakes in ouragricultural and irrigationdevelopment efforts, particularlymistakes that threaten long-termproductivity, or environmental andhuman health. The problems arenot insurmountable; they can besolved, provided appropriatestrategies and policies are followed.One of the important strategiesrelating to the prevention of water-borne diseases in irrigation schemesis the adoption of environmentalmanagement measures for diseasevector control. In this strategy,agriculturalists and engineers canplaya vital role. As lead players of

agricultural and water developmentteams, they can bring into thesystem appropriate measures tocombat water-borne diseases. Thispaper discusses the roleagriculturalists and engineers canplay in controlling water-bornediseases in agricultural andirrigation development projects.

Environmental factorsEnvironmental management forvector control refers to themodification and/or manipulationof environmental factors, or theirinteraction with man with a view topreventing or minimizing vectorpropagation and reducing man-vector pathogen contact.Environmental modification

consists of any physical change thatis permanent or long-lasting, suchas canal lining, drainage and landlevelling, while environmental

Others

Developmental inhibitors

Insecticides

manipulation refers to any plannedrecurrent activity aimed atproducing temporary conditionsunfavourable for vector breeding,such as the regulation of waterlevels in reservoirs, canal flushingand intermittent irrigation. Mod-ifications and/or manipulations ofthe environment in relation tohuman habitation or behaviour isalso considered a component ofenvironmental management, whichrefers to actions such as the sitingof settlements away from vectorbreeding sites and the mosquito-proofing of houses. Thecomponents of environmentalmanagement in the overall pictureof integrated mosquito control areillustrated in Figure 1.Most engineering and agronomic

practices fit well within theenvironmental modification andmanipulation components ofenvironmental management. It isinteresting to note that measuresaimed at improving irrigationsystem performance from theagricultural point of view, alsoalleviate the vector-borne disease

Marsh alteration(ditching, impoundment)

Zooprophylaxis

Basic sanitarymeasures

Filling, grading& drainage

Barrierplantings

Housescreening,bed nets

- Personalprotection

Chemosterilants

WATERLINES VOL.9 NO.2 OCTOBER 1990 7

Clean and well-maintained canals discourage snails and reduce the risk ofschistosomiasis infection.

hazard. It is vital to appreciate thatgood maintenance of irrigationschemes has both production andhealth benefits. Hence theimplementation of environmentalmanagement measures for vectorcontrol through the 'agriculturesector' should be relatively easy ifthe 'two-sided' benefits of suchmeasures are well-understood byengineers and agriculturalists alike.

Water storageStorage reservoirs are often acomponent of irrigation schemeenvironments. These might consistof large storage reservoirsassociated with hydro-power andwater regulation schemes, orrelatively small structures such asnight storage reservoirs, balancingreservoirs, or fish ponds.Because of their proximity to the

community, the small reservoirs canhave a marked impact on theincidence of vector-borne diseasesas compared to the large ones. Theintroduction and operation of smallreservoirs therefore calls for theparticular application ofappropriate management tech-niques. An especially importantaspect is that of maintenance. Asatisfactory storage structure, ifallowed to deteriorate, may createa serious health hazard.

Engineering measures relevant forvector control in the case of smallreservoirs include the appropriatedesign of dikes and dams, excessiveseepage prevention and facilities todrain the storage when required.Bank slope is an important

parameter in relation to the growthof marginal vegetation which mayform an ideal breeding ground formosquitoes and snails. A relativelysteep bank is therefore anadvantage, but slope stability anderosion problems should be takeninto account in designs.Larger reservoirs, generally at

the head of main canals andcontrolled by head gates andsluices, may also present seriousproblems. The more constant waterlevel and the low water velocitieson the margins provide anenvironment well-suited to snailsand the breeding of mosquitoes.The adoption of flushing procedures(to strand eggs and larvae), steeperslopes of banks protected with rip-rap, and the provision of screens tointake structures, are meansrecommended for vector control.

Water conveyanceOpen canal systems are the mostcommon means of waterconveyance in many irrigationschemes. Canal design is a major

factor in controlling the breedingof snails through a design providinga sufficiently high flow-velocity todetach the snails and a smoothboundary to reduce their ability tocolonize the banks. In Japan,replacing earth canals with concretelined ones in the schistosomiasisendemic rice-growing area of Kofuproved to be very successful ineradicating the disease. Canal liningalso benefits mosquito controlmeasures by reducing seepage,water table build-up, and thegrowth of aquatic and semi-aquaticvegetation on the margins ofirrigation schemes.

DrainageThe importance of drainage inagriculture has at last been realizedbut only at the cost of losing millionsof hectares of good agriculturallands due to water-table rise andsalinity and/or alkalinity. Theimportance of an appropriate andeffective drainage system issubstantiated not only from thepoint of view of agriculturalproduction, but also from thestandpoint of disease vectorcontrol.Lack of an appropriate drainage

system often results in waterloggingin the tail-end of a system and inlow-lying areas, and is likely tocreate an environment conduciveto vector multiplication. Equallybad is an inappropriately designedand ineffective drainage system.Drainage canals of large cross-sections and gentle slopes result inlow water-velocities, giving rise toconditions of sediment depositionand weed growth. These can befurther aggravated by fertilizerrunoff from the fields, providing anenvironment ideally suited to manydisease vectors. Standards of designand construction are major factorsin effective drainage, but equallyimportant is the maintenance of thedrains. A well-designed andmaintained drainage system with afree-flowing hydraulic regime willprevent the build-up of vectors notonly in the drainage system alonebut in the whole project area.

Water control structuresWater control structures areinstalled in water supply anddrainage canals in order to control,measure and divert water flow asrequired by the irrigation scheme.These structures include silt traps,drops, sluices, siphons, turnouts,

8 WATERLINES VOL.9 NO.2 OCTOBER 1990

$(I/,IIIt WIITEIt /ltlM/I'.(;/~••I.'I ". Ip.cl.,IIII:

intakes, offtakes, gates and manyothers. Each has a modifying effecton flow and a potential formaintaining a residual aquaticenvironment when the rest of theirrigation system is dry. This maythen provide a micro-habitat forvector production, or for sustaininga vector population between naturalor artificial wet seasons.Attempts have been made to

design water control structures thatwill freely drain the residual waterwhen flow in the canal system isstopped. At the MushandikeIrrigation Scheme in Zimbabwe,field-level experiments are beingconducted on the introduction of amodified drop structure that is freedraining, and on a new type of canalofftake structure to reduce themultiplication of vectors. The free-draining drop structure with itssuitably designed energydissipators, does not have the sumpwhich is common in most dropstructures. Thus standing waterdownstream of the drop is avoidedin the modified design, resulting ina potential for control of mosquitobreeding. Similarly, the offtakestructure that is being experimentedwith at Mashandike overcomesmany problems associated withtraditional offtake structures byallowing a free flow of water overthe weir and not reducing the flowvelocity upstream of the structure.As for any irrigation or drainagenetwork, maintenance of thesestructures is an important factor onwhich the ability to control bothwater and vector depends.Many on-farm management

practices, which fall within the areaof competence of agriculturalistsand farmers, can contribute to asignificant reduction in vectormultiplication without sacrificingyield or productivity. These willmainly be environmentalmanipulations as they aretemporary in nature but veryeffective in controlling vectorbreeding.

Water regimemanipulationsWater application to crops can beeffected by many methods. Somecommon irrigation methods are:basin; furrow; sprinkler; and micro.The type of irrigation methodfinally selected will depend on thecrop, field slope, soil, tillage andfarming practices, capitalinvestment, farmers' skills and

many other factors. Each systemhas a characteristic field-waterregime and hence has a definiteinfluence on vector multiplication.Basin irrigation with contiriuousflooding has a high risk of mosquitobreeding and snail infestation. Withtemporary flooding there are nodirect implications of vectorbreeding but during the rainyseason water may be present for alonger time and create a vectorhabitat. Similarly for furrowirrigation, if land levelling is poor,water may stagnate in the field andcause problems. In the cases ofsprinkler and micro irrigation thereare no vector breeding implicationsat all.Rice is predominantly irrigated

by the basin irrigation method andthe field is kept under standingwater most of the time. The mostusual method of rice production bysurface flooding and soil saturationprovides an ideal environment formany vector mosquito larvae andfor the snail intermediate host ofschistosomiasis.Although continuous flooding is

a common practice of riceirrigation, the rice plant does notrequire such a water regime for its

growth and the production of ricegrains. In fact, rice can be grownsuccessfully under non-floodedconditions and even under sprinklerirrigation. But growing rice undernon-flooded conditions requires animproved design of the deliverysystem, better water scheduling andgreater skill from the farmer.Alternate wetting and dryingappears to be a possibility which canbe adapted to most existingirrigation systems with minimumstructural changes and which has apotential to control the breeding ofmosquitoes.In the Yellow River Basin in

Henan Province, alternate wettingand drying was successfullyintroduced as a means of controllingthe breeding of Japaneseencephalitis mosquito in rice fields.Fifteen days after transplanting, therice fields were irrigated with ashallow layer of water so that itdisappeared within 24 to 48 hoursafter irrigation. The irrigationinterval varied between three to fivedays depending on the stage ofgrowth of the rice plant.Intermittent irrigation of rice as

a widely applicable and standardmethod of rice irrigation, however,

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has not yet been accepted by mostrice scientists and farmers. Thetopic was discussed in detail at anIRRIfPEEM collaborative meetingheld in Los Banos, Philippines in1987. The recommendation of themeeting on this subject is presentedbelow.

The effectiveness of alternative methods ofmanipulating on-field water regimes toeliminate or minimize breeding sites andreduce vector populations needs to bedetermined, and their impact on rice yieldsassessed for various soil types in differentrice-production systems. They are essentialfor devising water management methods thateffectively control vector-borne diseaseswithout reducing rice yield. Such evaluationsshould deal with intermittent irrigation aswelt as other irrigation practices.

Rice varieties that will permit theuse of intermittent irrigation orperiodic drainage should bedeveloped. The role of watercontrol infrastructure andmanagement, including rice-fieldlevelling, needs to be determinedfor the irrigation system as a wholeand for the farm level. The socio-economic implications of adoptingthe most promising methods alsorequire assessment.

Other on·farm practicesSeveral other on-farm managementpractices such as crop rotation,tillage, pesticide application andintegrated pest management, canbe important in the control ofvector-borne diseases in irrigationprojects. Agriculturalists andfarmers can thus playa lead role inintroducing practices which reducevector multiplication withoutsignificant loss to agriculturalproduction. For example in riceirrigation schemes, the introductionof upland, non-rice crops instead ofthe double cropping of rice is likelyto reduce vector breeding inendemic rice monocrop areas.Integrated pest management, asopposed to chemical pest control,has been found to be advantageousnot only in combatting agriculturalpests but also in vector control.Recent studies by IRRI (1988)

have shown that neem cake, anadditive with fertilizer used in ricefields, can be effective as a repellentto female mosquitoes searching foran appropriate location to deposittheir eggs and it also kills the larvae.Further research is needed toconfirm these effects, but thepotential benefits are evident.Many more agronomic practices

have been identified and are beinginvestigated. In all cases, the impact

of such practices on individualfarmers and the communityrequires evaluation.

Project improvementsA number of water resourcesdevelopment projects in the pasthave failed to meet their objectives,and produced far too many adverseimpacts, because of improperplanning. Most of these projectswere planned with narrowobjectives in mind and withoutconsideration for the manyimportant associated factors suchas environment, health and socialimpacts. Engineers andagriculturalists can play animportant role in planning, bringingto the notice of the planners,politicians and funding agencies,the need to adopt a holisticapproach in the planning process.They can contribute significantlyby drafting comprehensive terms ofreference for the planning studiesat the various stages of the planningphase, namely at the recon-naissance, pre-feasibility andfeasibility stages.The implementation of the

physical works form an importantphase in the development ofirrigation schemes. This follows afeasibility study, project appraisal,and selection and provision of fundsfor implementation.A recurring tragedy of

development is that environmentalconsiderations cease at the planningor assessment stage. In the past,there have been projects for whichcomprehensive feasibility reportsand preliminary designs, includingenvironmental health components,were prepared, but the environ-mental aspects were only partiallyconsidered, if not completelyignored, during final design andimplementation for reasons ofeconomy.The difficulty with many

environmental, health or socialinterventions is that they are noteasily quantifiable in terms oftangible benefits or economic value.Consequently, they are the first tobe dropped to improve theeconomic viability of a project, andhence the final design often fails toshow any environmental manage-ment component. The project isconstructed as per the final design,and specifications are rarelyevaluated during or afterconstruction against therecommendations made at theplanning stage. This is particularly

so in complex development projectswhere many plans are made and themost recent ones supercede olderones.Project construction is often

supervised by engineers andeconomists and the environmentalsupervision of construction is sadlylacking in many parts of the world.This situation can change only whenthe engineer takes the responsibilityto see that the final designincorporates all environmentalmanagement measures recom-mended at the planning phase, andthe construction is undertakenwithout any omissions. Theengineer can also playa crucial rolein checking the specifications ofconstruction that might influencethe project environment in relationto vector-borne diseases.

ManagementMany irrigation schemes have alsofallen short of their expectationsbecause of poor management. Aconsiderable amount of researchand development effort has goneinto improving the management ofirrigation schemes, and severalguidelines are available in this area.Most guidelines focus on operationand maintenance functions forincreasing crop yields, water-useefficiency, farmer income, and theeconomic efficiency of the schemes.Again, little attention is paid to thepotential for vector-borne diseasecontrol, yet it is interesting to notethat many environment mani-pulations in the context ofenvironmental management areindeed standard irrigation schemeoperation and maintenanceactivities. If operators pay properattention to these activities, thescheme can perform well not onlyin terms of production but also withrespect to the health and well-beingof the farming community. Projectengineers, agriculturalists, and theirstaff who manage the system shouldbe appropriately trained andmotivated to manage the system asa whole, and to the benefit of thefarming community. Operation andmaintenance functions should notbe limited to activities that aredirectly concerned with increasingagricultural production, butextended to include activities aimedat reducing vector-borne diseasesand ensuring environmentalprotection.

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Intersectoral collaboration between agriculturalists and health workers isessential. Here a health worker is supervising the dipping of nets in a malarialarea.

Extension and trainingSuccessful extension and trainingprogrammes in agricultural andirrigation projects aim at theachievement of an overall benefitto the farming population, includingincreased production, greatereconomic returns, better health,improved education, and a generalenhancement of the physicalenvironment, desires and expect-ations. It is the aim of agriculturalextension and education experts toinfluence the on-farm leveltechnicians and farmers to adoptcertain improved and desirablepractices that will contribute toincreased agricultural productionand better family and communityliving. The management andcontrol of vectors and theprevention of associated diseases inagricultural and irrigation projectscan be an integral part of theagricultural extension objectives.Current agricultural extension

and training programmes in mostcountries do not respond to healthproblems or the needs of ruralcommunities. The major reason isthe lack of communication andco-ordination of the agriculturaland engineering ministries withhealth ministries. Without formalcollaboration at higher levels, itwould be difficult for extensionworkers to initiate health-orientedactivities in a project area. Thus animportant role of agriculturalistsand engineers emerges from thisanalysis, namely, the creation ofrelevant co-ordinating mechanismsto secure co-operation ofgovernment departments, stateinstitutions and local authorities.Perhaps these can best be initiatedand followed up by agriculturalistsand engineers in the planning andimplementation of an integratedextension programme. Theinclusion of health and vectorcontrol components in an integratedextension package can contributesignificantly to the success ofagricultural and irrigation dev-elopment projects and in particularalleviate the health hazards of thefarming community.

SummaryThe demand for food will continueto increase as populations grow andconsumption patterns change.Agricultural development, bothrainfed and irrigated, receives toppriority in international technicalco-operation and investment pro-

grammes, as well as in nationaldevelopment efforts. Irrigatedagriculture, by virtue of its highproduction potential and thestabilization of production, assumesa high-ranking position in thedevelopment of world agriculture.Agricultural development, how-

ever, if planned and implementedin a narrow perspective will notproduce the desired goal. To makeproduction efforts sustainable, aholistic approach is essential and inthis approach the incorporation andimplementation of health safe-guards to protect the farmingcommunity are vital. Manyagricultural and irrigation develop-ment projects have failed in thepast, through lack of forethought.It is now recognized that healthcomponents, particularly measuresto control vector-borne diseases inagriculture and irrigation devel-opment schemes, should beintegrated in the projects' overallplanning, development andmanagement phases. Towardsachieving this, agriculturalists and

engineers play an important role.By developing new and innovativemethods of engineering andagricultural technology, assisting inthe appropriate and necessaryplanning, design and managementof projects, and establishing inter-sectoral collaboration and inte-grated agricultural and healthextension and training programmes,agriculturalists and engineers canand must play a vital role inpreventing adverse health impactson farming communities. The taskof the agriculturalists and engineersis to ensure that the developmentprocess takes into account bothpositive and negative impacts andapplies the most appropriatemeasures in combating undesirableeffects, to ensure maximum benefitsfrom investment and developmentefforts.

A. Kandiah is with the PEEM Secretariat,Land and Water Development Division,FAO, Via delle Terme di Caracalla, 00100,Rome, Italy.

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